Fuel may be directly injected to an engine cylinder to improve mixture preparation and to reduce cylinder charge temperature. The amount of time a direct fuel injector is activated may be a function of pressure of fuel supplied to the direct fuel injector, engine speed, and engine load. The pressure of fuel supplied to the direct fuel injector may be elevated by transferring heat from an engine to fuel as fuel is delivered to a fuel rail supplying the direct fuel injectors. The higher fuel pressure may increase a flow rate of fuel through the direct injector such that a fuel pulse width supplied to operate the direct fuel injector may need to be adjusted to a short duration of time (e.g., less than 500 micro-seconds). However, operating the direct fuel injector with a short pulse width voltage command may cause the direct fuel injector to operate in its non-linear or ballistic operating range where the amount of fuel injected may vary substantially for small changes in the fuel pulse width. Additionally, deposits formed at the injector's nozzle may also contribute to an unintended amount of fuel flowing through the direct fuel injector. Consequently, the direct fuel injector may not provide a desired amount of fuel when shorter duration pulse widths are applied to the direct fuel injector.
The inventors herein have recognized the above-mentioned disadvantages and have developed a method for fueling a cylinder, comprising: supplying a first pulse width and a second pulse width to a fuel injector during a cylinder cycle, where the first pulse width operates the fuel injector in a non-linear operating region, and where the second pulse width operates the fuel injector in a non-ballistic operating region; adjusting a control parameter of the fuel injector in response to exhaust lambda; and operating the fuel injector based on the adjusted control parameter.
By supplying two pulse widths to a fuel injector during a cycle of a cylinder receiving fuel from the fuel injector, it may be possible to provide the technical result of adjusting a fuel injector transfer function or gain without having to operate the cylinder with an air-fuel ratio that may be leaner or richer than is desired. In particular, a first pulse width supplied to a fuel injector may be short enough in duration to operate the fuel injector in its non-linear low flow region. A second pulse width supplied to the fuel injector during a same cylinder cycle may be long enough to operate the fuel injector in its linear operating range so that a fuel amount closer to a desired fuel amount may be supplied to the cylinder during the cylinder cycle. Consequently, if fuel supplied by the fuel injector in response to the first pulse width is greater or less than a desired amount, the aggregate air-fuel mixture during the cylinder cycle may be less affected because a greater amount of a desired fuel amount to be injected to the cylinder may be provided via the second pulse width operating the fuel injector.
The present description may provide several advantages. In particular, the approach may reduce engine air-fuel errors. Additionally, the approach may allow a fuel injector to be operated at pulse widths that were heretofore avoided because of non-linear fuel injector behavior. Further, the approach may reduce engine emissions and improve catalyst efficiency.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.